Biomedical subjects

M García-Fiñana

Publications and source records attributed to M García-Fiñana.

6 recordsLinked to original sources

PubMed2006

Confidence intervals in Cavalieri sampling.

The aim of this study is to derive a formula that allows the prediction, from a Cavalieri data sample, of an appropriate confidence interval for a parameter Q. Two different approaches are used to address the problem. The first approach is to investigate whether the asymptotic distribution of the Cavalieri estimator exists when the sampling period T tends to zero. In particular, the distribution of the standardized version of the Cavalieri estimator z(T) is analysed for a measurement function f whose smoothness constant is an integer number m. The analysis reveals that when the first noncontinuous derivative of f, f((m)), exhibits a unique discontinuity, the asymptotic distribution of z(T) exists and it has a bounded support. An analytical expression of the distribution is derived for the cases m = 0 and 1. However, when f((m)) has two or more discontinuities, the asymptotic distribution of z(T) does not exist and its support may be unbounded. In the second approach, a generalized version of the refined Euler Mac-Laurin summation formula, valid for measurement functions with a fractional, rather than just an integer, smoothness constant, is applied to the Cavalieri estimator. As a result, a formula that predicts a lower and upper bound for the true parameter is derived for small T. This bound prediction formula is applied to Cavalieri data samples of human cerebral cortex. In particular, for sample sizes n = 8, 12 and 16, the true volume of cerebral cortex is bounded by relative distances 8%, 4% and 2% of the Cavalieri estimate, respectively.

Journal Article↗

PubMed2006

Effect of ultra-high molecular weight polyethylene thickness on contact mechanics in total knee replacement.

One of the important design parameters in current knee joint replacements is the thickness of the ultra-high molecular weight polyethylene (UHMWPE) tibial insert, yet there is no clear definition of the upper limit of the 'thick' polyethylene insert. Using one design knee implant and subjecting it to the physiological loads encountered throughout the gait cycle, measurements of the lengths of contact imprints generated were compared with the corresponding theoretical predictions for different insert thicknesses under the same applied load. Multiple regression analysis was applied to test whether the dimensions of contact imprints are influenced by UHMWPE thickness. Good agreement was obtained between the theoretical predictions and the experimental measurements of the dimensions of contact imprints when the knee was at 60 degrees flexion. Therefore, it was possible to estimate the contact pressure at the articulating surface using the theoretical model. Contact imprint dimensions increased with increasing applied load. Statistical analysis of the experimental data revealed that, at 0 degree flexion, the overall imprint dimensions increased as the UHMWPE thickness increased from 8 to 20 mm. However, the increment was not significant when the thickness subinterval 10-15 mm was considered. Furthermore, at 60 degrees flexion, thickness was not a significant factor for the overall imprint dimensions. No evidence was found from the data to suggest that an increment in polyethylene thickness over 10 mm would significantly reduce the contact imprint dimensions. These findings suggest that thicker inserts can be avoided, as they require unnecessary bone resection.

Acetabulum↗

PubMed2006

Degree of hippocampal atrophy is related to side of seizure onset in temporal lobe epilepsy.

BACKGROUND AND PURPOSE: Temporal lobe epilepsy (TLE) is associated with pathologic changes in hippocampal physiology and morphology. Our aim was to quantify volume reduction of the right and left hippocampus in patients with TLE and to investigate whether the degree of hippocampal atrophy is related to the side of seizure onset. METHODS: The volume of the right and left hippocampus was estimated for 50 controls and 101 patients with TLE, by applying the unbiased Cavalieri method on MR images. RESULTS: Pairwise comparisons, within a multivariate analysis of variance and adjusted by using the Bonferroni correction, revealed that both right and left hippocampal volumes were, on average, significantly smaller in patients with right-sided seizure onset (R-patients) relative to those of controls (P < .001 and P = .04, respectively). Furthermore, left hippocampal volume was significantly smaller in patients with left-sided seizure onset (L-patients) compared with controls (P < .001), but the right-sided hippocampal volume was not significantly smaller (P = .71). Moreover, a correlation analysis revealed that the strong linear association between the right and left hippocampal volumes existing in the control population (r = 0.73) is partially lost in patients with TLE (r < or = 0.48), and this loss in correlation appears to be more pronounced in L-patients than in R-patients. CONCLUSION: Our MR imaging results suggest that although the major damage in patients with TLE is located in the hippocampus ipsilateral to the side of seizure onset, R-patients are more likely to have bilateral hippocampal volume reduction. These findings support the hypothesis that cerebral hemispheres may not only differ in their functionality organization but also in their vulnerability to a neurologic insult.

Adult↗

PubMed2004

Quantification of tumour response to radiotherapy.

In 1979, the World Health Organization (WHO) established criteria based on tumour volume change for classifying response to therapy as (i) progressive disease (PD), (ii) partial recovery (PR), and (iii) no change (NC). Typically, the tumour volume is reported from diameter measurements, using the calliper method. Alternatively, the Cavalieri method provides unbiased volume estimates of any structure without assumptions about its shape. In this study, we applied the Cavalieri method in combination with point counting to investigate the changes in tumour volume in four patients with high grade glioma, using 3D MRI. In particular, the volume of tumour within the enhancement boundary, the enhancing abnormality (EA), was estimated from T(1) weighted images, and the volume of the non-enhancing abnormality, (NEA) enhancing abnormality, was estimated from T(2) relaxation time and magnetic transfer ratio tissue characterization maps. We compared changes in tumour volume estimated by the Cavalieri method with those obtained using the calliper method. Absolute tumour volume differed significantly between the two methods. Analysis of relative change in tumour volume, based on the WHO criteria, provided a different classification using the calliper and Cavalieri methods. The benefit of the Cavalieri method over the calliper method in the estimation of tumour volume is justified by the following factors. First, Cavalieri volume estimates are mathematically unbiased. Second, the Cavalieri method is highly efficient under an appropriate sampling density (i.e. EA volume estimates can be obtained with a coefficient of error no higher than 5% in 2-3 min). Third, the source of variation of the volume estimates due to disagreements between observers, and within observer, is much greater in the positioning of the calliper diameters than in the identification of the tumour boundaries when applying the Cavalieri method. Additionally, the error prediction formula, available to estimate the coefficient of error of Cavalieri volume estimates from the data, allows us to establish more precise classification criteria against which to identify potentially clinical significant changes in tumour volume.

Brain Neoplasms↗

PubMed2000

Estimation of body composition in muscular dystrophy by MRI and stereology.

We have applied the Cavalieri method of modern design stereology with magnetic resonance imaging for estimating the volume of whole-body muscle and fat compartments in four patients with muscular dystrophy, a patient with myopathy, five controls, an anorexic subject, and a body builder. Detailed systematic series (ie, 50) of axial MR images (T1-weighted, TR/TE 400/10 msec) were obtained throughout the whole body of each subject. The results showed that 15, 20, and 35 axial sections through the body are sufficient to secure coefficients of error (CEs) on the estimates of total muscle and fat volume of around 10%, 5%, and 3% respectively in muscular dystrophy patients and controls. The mean normalized volumes of muscle in four muscular dystrophy patients were decreased by 27% (t-test: P < 0.05), and those of total fat were increased by 12% (t-test: P > 0.05) relative to controls. The Cavalieri method provides a direct, efficient, and mathematically unbiased approach for studying human body compartments and may have application in assessing treatment efficacy in patients with muscular dystrophy. J. Magn. Reson. Imaging 2000;12:467-475.

Adipose Tissue↗

PubMed1999

Estimation of breast volume and its variation during the menstrual cycle using MRI and stereology.

Unbiased estimates of breast volume may be obtained in vivo from systematic series of MR images acquired in accordance with the Cavalieri method of modern design-based stereology. The method does not require any assumptions to be made regarding breast shape. If point counting techniques are used to obtain the required breast section areas estimates, 10-15 min analysis (i.e. counting about 250 points on 12 to 16 images) ensures that the contribution of sectioning and point counting to the coefficient of error (CE) on the volume estimate is less than 3%. The methods were applied to measure breast volume in 15 healthy females aged between 22 and 44 years (mean 31.7 years; SD 8.2 years). One subject was studied on every fourth day during two consecutive cycles. The other 14 subjects were studied on three occasions corresponding to menses, ovulation and pre-menses during a single menstrual cycle. Repeat imaging after repositioning on three occasions within a period of 30 min and also at three different times of day for a single subject, both yielded a coefficient of variation (CV) of less than 3% in the estimation of breast volume. ANOVA indicates that there is no significant difference between the mean volume of the left and the right breast (p = 0.294). The mean volume of the left breast is 561 ml (95% confidence interval (CI): 553 ml, 569 ml) and the mean volume of the right breast is 567 ml (95% CI: 559 ml, 576 ml). There are highly significant differences between the three named stages of the menstrual cycle (p < 0.0005), whereby the mean volume at ovulation is 5.5% less than the mean volume at menses (95% CI: 3.0%, 7.9%) and the mean volume pre-menses is 8.1% greater than the mean volume at menses (95% CI: 5.3%, 10.9%). Overall, the volume of each breast varies by an average of 76 ml (95% CI: 61 ml, 92 ml) during the menstrual cycle, which corresponds to 13.6% of the volume at menses (95% CI: 13.3%, 13.8%). No significant interaction was found between the relative volumes of the left and right breast and the stage of the menstrual cycle (p = 0.277), nor between subjects and stages of cycle (p = 0.296). However, a significant interaction was observed between the volume of the left and right breasts in different subjects (p < 0.005). The average difference in the volume of the left and right breasts of all 15 subjects is 39.7 ml (95% CI: 21.3 ml, 58.1 ml), which is 7% of average breast volume and approximately 50% of the average variation in the volume of the breast during the menstrual cycle.

Adult↗